In a semiconductor device manufacturing process or a flat panel display (FPD) manufacturing process, there is performed an etching process of etching an oxide film of a semiconductor wafer serving as a processing target substrate. During the etching process, a part of resist is corroded with an etching liquid to be modified, and a polymer (resist residue) is formed to remain on the semiconductor wafer. Therefore, after the etching process, a cleaning process is performed on the wafer with a chemical liquid to remove the polymer remaining on the semiconductor wafer. By way of example, a mixed chemical liquid containing sulfuric acid, hydrogen peroxide solution, hydrofluoric acid, and the like is used as the chemical liquid.
Patent Document 1: Japanese Patent Laid-open Publication No. 2002-343762
Generally, when sulfuric acid is mixed with water, an exothermic reaction occurs. Therefore, if pure water is mixed with sulfuric acid, a temperature of the mixed solution is increased. Meanwhile, it is appropriate for a mixed chemical liquid including pure water, sulfuric acid, hydrogen peroxide solution, and hydrofluoric acid to be used around room temperature.
In a cleaning apparatus described in Patent Document 1, pure water, hydrogen peroxide solution, and sulfuric acid are supplied into a pre-mixing tank and then a mixing pump is operated. Thus, the sulfuric acid is concentrated on a certain portion of an inside of the pre-mixing tank and a temperature of the mixed chemical liquid within the pre-mixing tank tends to highly increase at this portion. In this case, it takes a lot of time to cool the mixed chemical liquid having an increased temperature, and, thus, it is difficult to shorten a time for producing the mixed chemical liquid.